Port control

ABSTRACT

A locator of a surgical port of a surgical robot system, the surgical robot system comprising an instrument attached to a robot arm, the instrument having an instrument shaft able to pass through the surgical port to a surgical site, the locator comprising: an interface configured to couple to the surgical port; a mechanism configured to permit relative linear and/or rotational motion of the interface and the instrument shaft; and a controller comprising a processor operable to estimate the position of a part of the robot arm, the controller configured to control the mechanism in dependence on the estimated position of the part of the robot arm such that as the robot arm retracts the instrument from the patient, the locator moves the port away from the robot arm and provides a reaction force to keep the port in place.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application under 35 U.S.C. § 120 ofU.S. patent application Ser. No. 16/533,674, filed Aug. 6, 2019, whichis a continuation application under 35 U.S.C. § 120 of U.S. patentapplication Ser. No. 15/355,850, filed Nov. 18, 2016, and claims benefitunder 35 USC § 119 of United Kingdom Application No. 1520754.1, filedNov. 24, 2015. The contents of these applications are herebyincorporated by reference in their entirety.

This invention relates to the positioning of surgical ports.

BACKGROUND

FIG. 1 illustrates part of an apparatus used for conventional roboticsurgery. The apparatus comprises a robot arm 1, only the distal end ofwhich is shown in FIG. 1. A rail 2 extends from the distal end of thearm towards a patient, whose skin is indicated at 3. At the end of therail is a surgical instrument 4 which passes into the patient forperforming surgery. The instrument enters the patient through anincision in the skin. To keep the incision clear, and to avoid thepatient's skin being torn when the instrument is moved, a port 5 islocated in the incision. The port is carried by the rail 2. The port isfree to slide along the length of the rail as indicated by arrow 6, andthe port clips into the incision. Because the port adheres to the tissuearound the incision, when the robot arm 1 moves the instrument into andout of the patient during surgery a force is applied to the port. Thisforce moves the port along the rail so that the port can stay in placein the incision.

This approach has a number of problems. First, the port needs somemechanism to bind to the incision in order that it will stay in placewhen the instrument is moved. This mechanism can enlarge the incision orcause damage to the tissue around the incision. Second, if the port isnot properly secure in the incision it can be ripped out of the incisionwhen the robot moves the instrument. This can again damage the incision.Finally, the mechanism relies on forces being applied to the port by thetissue around the incision. These forces can themselves cause damage tothe tissue at the incision.

Similar problems arise in non-robotic laparoscopic surgery. However, inmanual surgery the surgeon is standing next to the patient and cannormally see or feel the signs of a port becoming loose or of excessiveforce being applied to the port. In robotic surgery the force feedbackthat a surgeon gets from a robot may be comparatively weak or imprecise,and with many other displays to look at the surgeon might not keep theports under constant observation.

There is a need for an improved way of locating surgical ports.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided a locator ofa surgical port of a surgical robot system, the surgical robot systemcomprising an instrument attached to a robot arm, the instrument havingan instrument shaft able to pass through the surgical port to a surgicalsite, the locator comprising: an interface configured to couple to thesurgical port; a mechanism configured to permit relative linear and/orrotational motion of the interface and the instrument shaft; and acontroller comprising a processor operable to estimate the position of apart of the robot arm, the controller configured to control themechanism in dependence on the estimated position of the part of therobot arm such that as the robot arm retracts the instrument from thepatient, the locator moves the port away from the robot arm and providesa reaction force to keep the port in place.

There may be provided a locator for a surgical port, the locatorcomprising: an interface for attachment to a portion of the surgicalport; a mechanism for permitting linear relative motion of the interfaceand a robot arm; and a controller for controlling the position of theinterface relative to the robot arm in dependence on the position of therobot arm; in which the mechanism is an engaging mechanism for engagingwith an instrument shaft of an instrument coupled to the robot arm; orin which the locator comprises a seat for attachment to the robot armand the mechanism links the seat and the interface, the mechanismcomprising one of a single member allowing motion over the full extentof the linear relative motion and an articulated mechanism.

Suitably the mechanism permits linear relative motion of the seat andthe interface.

There may be provided a locator for a surgical port, the locatorcomprising: an interface for coupling to the surgical port; an engagingmechanism for engaging with an instrument shaft of a robot arm to permitlinear relative motion of the interface and the robot arm; and acontroller for controlling the position of the interface relative to therobot arm in dependence on the position of the robot arm.

The interface may be coupled to a port body of the surgical port.Suitably the interface is attached to the port body. Suitably theinterface is attached to the surgical port.

Suitably the controller is for controlling the position of the interfacerelative to the robot arm such that it is separately controlled from thecontrol of the robot arm. Suitably the controller is for controlling theposition of the interface relative to the robot arm such that it isseparately controlled from the position of the robot arm. In otherwords, the interface can be controlled separately from the robot arm.The interface may move at the same time as the robot arm, but it neednot do so.

Suitably the engaging mechanism is arranged to frictionally engage withthe instrument shaft (or tool shaft). Suitably the engaging mechanismcomprises frictional engagement means for frictionally engaging with theinstrument shaft (or tool shaft). The frictional engagement means maycomprise a roller. Suitably the frictional engagement means comprisesmore than one roller, such as opposing rollers for engaging withopposing sides of the instrument shaft. The engaging mechanism maycomprise one or more rollers for frictionally engaging with opposingsides of the shaft. This can increase the stability of movement of thesurgical port along the instrument shaft. The engaging mechanism maycomprise a resilient portion for resiliently engaging with the shaft,for example to assist the frictional engagement between the engagingmechanism and the shaft. Suitably the frictional engagement means isresilient. At least one roller may be resilient.

The engaging mechanism may comprise gears. Suitably the gears are forpermitting engagement of the engaging mechanism with the instrumentshaft. Suitably the gears permit control of the relative position of theengaging mechanism and the instrument shaft. The instrument shaft may beprovided with spaced ridges for coupling with the gears so as to permitthe engaging mechanism to be driven relative to the shaft. In this waythe coupling between the gears and the ridges can act as a rack andpinion. This arrangement can provide increased control over the relativemovement between the interface and the robot arm (e.g. between theinterface and the instrument shaft). For example this might reduce orprevent slipping of the engagement mechanism relative to the instrumentshaft.

Suitably the locator comprises a driver for altering the configurationof the engaging mechanism. Suitably the driver is arranged for drivingthe frictional engagement means. Suitably the driver is arranged fordriving the gears.

Suitably the locator is arranged to determine the relative movementbetween the interface and the instrument shaft and/or the location ofthe interface on the instrument shaft relative to a known location ofthe interface relative to the instrument shaft. The known location maybe at the distal end of the instrument shaft. The known location may beat the proximal end of the instrument shaft.

Suitably the locator is arranged to sense the distance between theinterface and a portion of the robot arm. Suitably the locator comprisesa distance sensing means for sensing the distance between the interfaceand a portion of the robot arm. This can allow the locator to determinethe location of the surgical port along the instrument, for example thedistance of the surgical port from the proximal end of the instrumentshaft. The distance sensing means may be a sensor. Suitably the distancesensing means is arranged to sense the distance wirelessly. The sensormay be a light sensor. Suitably the sensor is a laser sensor.

The locator may comprise a locator body. The distance sensing means, forexample the sensor, may be provided in a position spaced from thelocator body, for example on a portion of the robot arm. Suitably thedistance sensing means is provided on the locator body.

The locator may comprise a connection for receiving power from anexternal source. Suitably the locator comprises a power source, such asa battery. The locator may comprise a wired connection to enablecommunication with a remote device. Suitably the locator comprises awireless communication module for enabling wireless communication with aremote device. The remote device may be a portion of a robotic surgicalsystem, for example a module thereof. Suitably the wirelesscommunication module is arranged to communicate with the remote deviceusing at least one of radio frequency radiation and infra-red radiation.Other types of wireless communication would also be possible. Thelocator body may comprise the wired connection and/or the wirelesscommunication module.

Suitably the locator body comprises the controller. In this way, thelocator can act autonomously to move the surgical port in response tomovements of the robot arm.

There may be provided a locator for a surgical port, the locatorcomprising: a seat for attachment to a robot arm; an interface forcoupling to the surgical port; a mechanism linking the seat and theinterface, the mechanism permitting linear relative motion of the seatand the interface; and a controller for controlling the position of theseat relative to the interface in dependence on the position of therobot arm; wherein the mechanism comprises one of a single memberpermitting the linear relative motion and an articulated mechanism.

There may be provided a locator for a surgical port, the locatorcomprising: a seat for attachment to a robot arm; an interface forcoupling to the surgical port; a mechanism linking the seat and theinterface, the mechanism permitting linear relative motion of the seatand the interface, the mechanism comprising a single member permittingthe linear relative motion; and a controller for controlling theposition of the seat relative to the interface in dependence on theposition of the robot arm.

Suitably the interface is attached to the surgical port.

Suitably the controller is for controlling the position of the seatrelative to the interface such that it is separately controlled from thecontrol of the robot arm. Suitably the controller is for controlling theposition of the seat relative to the interface such that it isseparately controlled from the position of the robot arm.

Suitably the single member is an extensible member for extending so asto permit the linear relative motion. Suitably the extensible member maybe made of an extensible material, such as an expandable material. Theextensible member may have a concertina-type form. Suitably theextensible member is an inflatable member, such as an inflatable sheath.Suitably the inflatable sheath is arranged to enclose at least a portionof the instrument or tool coupled to the robot arm. The inflatablemember may be an inflatable bag for enclosing at least a portion of theinstrument coupled to the robot arm. The extensible member may be partof a sterile drape, such as a sterile drape that covers at least aportion of a robotic surgical system for providing a sterile barrierbetween the robotic surgical system and a surgical site. The steriledrape may cover at least a portion of the robot arm.

Suitably the extensible member comprises an inlet port. The inlet portcan be for allowing fluid such as gas into an interior of the extensiblemember. The extensible member may be arranged to extend in response tothe inlet of fluid into the interior. The inlet port may be connectableto a fluid port on the robot arm. In this way, the extensible member canreceive fluid through the robot arm so as to enable the extension of theextensible member. The extensible member may comprise an outlet port.The outlet port can be for allowing fluid such as gas to escape from theinterior of the extensible member. This can facilitate the deflation orshrinking of the extensible member. The inlet port of the extensiblemember may provide an outlet fluid path from the inside of theextensible member. This outlet fluid path may additionally oralternatively provide for fluid to escape from the interior of theextensible member.

The inlet port of the extensible member may comprise, or be associatedwith, a pump for pumping fluid through the port. This can allow fluid tobe pumped into and/or out of the extensible member, for example toinflate (expand) and/or deflate (contract) the extensible member. Thiscan provide control over the amount by which the extensible memberextends, and so the position of the seat relative to the interface.

The extensible member may be resilient. The extensible member may bemade from a resilient material. This can provide a resistance to theextension of the extensible member, which can enable a more positivedetermination of its extension. It can also facilitate deflation orcontraction of the extensible member by assisting in the outflow offluid from its interior.

The source of fluid for extending the extensible member may be the sameas the source of fluid for insufflating a surgical site.

The extensible member may be arranged to extend by at least one ofunfurling and uncoiling. The extensible member may be a coiled member,such as a spiral tape, for example a metal tape.

The locator may comprise an extensible member housing for housing theextensible member, for example when it is in a non-extended state,and/or when it is at least partially retracted. For example, the housingmay house the coiled member, such as the coil of tape. Suitably thehousing is provided on a portion of the robot arm. This can minimise thesize and/or weight of the surgical port and its attachments.

The locator may comprise a driver for altering the configuration of theextensible member. The driver may comprise the pump.

There may be provided a locator for a surgical port, the locatorcomprising: a seat for attachment to a robot arm; an interface forcoupling to the surgical port; a mechanism linking the seat and theinterface, the mechanism being articulated and permitting linearrelative motion of the seat and the interface; and a controller forcontrolling the position of the seat relative to the interface independence on the position of the robot arm.

The robot arm may have a series of articulations along its length forpermitting movement of the distal end of the robot arm relative to theproximal end of the robot arm. The seat may be attached to the robot armproximally of (i.e. further from the distal end of the arm than) themost distal articulation of the arm.

The most distal articulation of the arm may permit rotation about anaxis substantially parallel to an axis along which the mechanism permitsthe linear relative motion, such as the linear relative motion of theseat and the interface.

Suitably the articulated mechanism comprises a plurality of jointsbetween the seat and the interface. Each of the joints may be a revolutejoint or a prismatic joint. Any combination of revolute joints andprismatic joints may be used. Other joint types are also possible, inany combination.

The locator may comprise a driver for applying a force between the seatand the interface to alter the configuration of the mechanism. Thecontroller may comprise the driver. The driver may comprise a motor, forexample an electric motor. The driver may comprise a hydraulically orpneumatically operable piston.

The mechanism may permit solely linear relative motion of the seat andthe interface or of the robot arm and the interface.

There may be provided a locator for a surgical port, the locatorcomprising: a base for attachment to a portion of a patient support; aninterface for coupling to the surgical port; a support mechanism linkingthe base and the interface, the support mechanism permitting at leastone of translational and rotational movement of the interface relativeto the base; and a controller for controlling at least one of theposition and orientation of the interface relative to the base independence on the position of the robot arm.

Suitably the interface is attached to the surgical port. Suitably thecontroller is for controlling at least one of the position andorientation of the interface relative to the base such that it isseparately controlled from the control of the robot arm. Suitably thecontroller is for controlling at least one of the position andorientation of the interface relative to the base such that it isseparately controlled from the position of the robot arm.

Suitably, where the support mechanism permits one of the translationaland rotational movement of the interface relative to the base, thecontroller is arranged to control a respective one of the position andorientation of the interface relative to the base. Suitably the supportmechanism permits both translational and rotational movement of theinterface relative to the base and the controller is for controllingboth the position and orientation of the interface relative to the basein dependence on the position of the robot arm.

In other words, the support mechanism can allow the interface, and alsofor example a surgical port coupled to the interface, to be moved to adesired location or position. The support mechanism may provide stablesupport at this location. In other words, once the interface has beenpositioned as desired, the support mechanism may restrict undesiredfurther movement from this position. The support mechanism may bearranged to permit further desired movement. Suitably the supportmechanism comprises a lock. The lock may have a locked and an unlockedconfiguration. Suitably in the unlocked configuration the lock willpermit movement of the support mechanism. The movement permitted by theunlocked configuration may include at least one of translational androtational movement. Suitably the support mechanism permitstranslational movement of the interface relative to the base when thelock is in the unlocked configuration.

Suitably in the locked configuration the lock will restrict or preventmovement of the support mechanism. The movement restricted by the lockedconfiguration may include at least one of the translational androtational movement. Suitably the support mechanism restrictstranslational movement of the interface relative to the base when thelock is in the locked configuration.

The support mechanism may comprise a support arm for permitting movementof the interface relative to the base. Suitably the support arm is anarticulated support arm. Suitably the support arm comprises at least onejoint. The lock may be arranged to permit and/or restrict movement ofthe at least one joint or articulation of the support arm.

The support mechanism may comprise a belt such as a solid belt forlinking the base and the interface. This can provide structuralrigidity. The structural rigidity may be provided by the rigidity of thesupport mechanism itself, or by the holding of an object by the supportmechanism. That is to say, a non-rigid belt can provide structuralrigidity by, for example, being held against an object such as apatient. The support mechanism can be held against the object bytension.

The support mechanism may comprise a rotational mechanism permittingrotation of the interface relative to the base. The rotational mechanismmay comprise a gimbal system.

The support mechanism may comprise a driver for driving the supportmechanism. Driving the support mechanism can include altering theconfiguration of the support mechanism. Suitably the driver is arrangedto alter the translational configuration of the interface relative tothe base. Suitably the driver is arranged to alter the rotationalconfiguration of the interface relative to the base. The gimbal systemmay comprise the driver. The gimbal system may be driven by the driverto control the orientation of the gimbal system. In this way theorientation of the surgical port can be controlled.

The locator may have a surgical port attached to the interface.

There may be provided a surgical robot having: a robot arm, and alocator as defined in any aspect above coupled to the robot arm. Thelocator may be attached to the robot arm.

The surgical robot may comprise a surgical tool or instrument attachedto the robot arm. A portion of the surgical tool may be arranged to passthrough the surgical port. The surgical tool may be substantiallyunsupported by the locator.

There may be provided a surgical robot having: a robot arm, a surgicaltool or instrument attached to the robot arm, and a locator as definedin any aspect above coupled to the instrument. The locator may beattached to the instrument.

The controller may comprise a processor operable to estimate theposition of a part of the arm and to set the position of the seatrelative to the interface in dependence on the estimated position. Thecontroller may comprise a processor operable to estimate the position ofa part of the arm and to set the position of the interface relative to aportion of the arm in dependence on the estimated position. Thecontroller may comprise a processor operable to estimate the position ofa part of the arm and to set the position and/or orientation of theinterface relative to the base in dependence on the estimated position.

The surgical port may comprise an inlet port. Suitably the inlet portprovides a fluid path into a port body of the surgical port. The portbody may comprise a chamber. Suitably the inlet port is in fluidcommunication with the chamber. Suitably the surgical port comprises anoutlet port. The outlet port may provide a fluid communication path frominside the port body, such as from inside the chamber, to an environmentoutside the surgical port. This can allow the inlet to communicate, viathe outlet, with a surgical site. Fluid, such as gas, for example carbondioxide, can be provided through the inlet so as to provide the fluid tothe surgical site.

Suitably the surgical port comprises a first valve, such as a one-wayvalve, in communication with a first fluid path between the inlet portand the outlet port. This can restrict fluid flow to occur in onedirection, such as from the inlet towards the outlet. Suitably thesurgical port comprises a second valve, such as a one-way valve, locatedin a second fluid flow path between the first fluid path and themechanism. This can restrict the fluid to flow along the first flowpath. This can help prevent fluid leaking out of the surgical port alongthe second flow path.

Any one or more feature of any aspect above may be combined with any oneor more feature of any other aspect above. These have not been writtenout in full here merely for the sake of brevity.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only withreference to the accompanying drawings. In the drawings:

FIG. 1 shows a prior art surgical port;

FIG. 2 shows a locator coupled to a surgical port;

FIGS. 3a-3b show another locator coupled to a surgical port with thelocator in relatively (a) contracted and (b) extended configurations;

FIGS. 4a-4b show another locator coupled to a surgical port with thelocator in relatively (a) contracted and (b) extended configurations;

FIGS. 5 to 7 show other locators coupled to surgical ports;

FIG. 8 illustrates a control device for the locator of any of FIGS. 2 to7;

FIG. 9 illustrates surgical ports; and

FIGS. 10 and 11 illustrate logic used by a controller.

DETAILED DESCRIPTION

The port carriers or port locators illustrated in the figures allowcontrol of the position and/or orientation of a surgical port so as tomaintain a desired relationship between the surgical port and a robotarm (and therefore also between the surgical port and an instrument ortool shaft coupled to the robot arm).

In one example, the position of the surgical port can be controlled asthe robot arm is moved towards the surgical port. For example, the toolshaft may be moved through the surgical port in an inward direction at agiven desired rate of movement. The position of the surgical port can becontrolled to move towards the robot arm at the same desired rate ofmovement so that the shaft can pass smoothly through the surgical portwithout disturbing its position.

In another example, the orientation of the surgical port can becontrolled as the robot arm changes its orientation to more easilyaccommodate the shaft passing through the surgical port.

Referring to FIG. 2, the port carrier or port locator is coupled to asurgical port 10. The locator is coupled to the port 10 by an interface12. The locator comprises an engaging mechanism 14 for engaging with thetool shaft 16; a wireless communications module (shown schematically at22) for allowing communication between the locator and a remote devicesuch as a robotic surgical system controller; and a motor (shownschematically at 24) for driving the engaging mechanism 14.

In the example shown, the engaging mechanism comprises a pair ofopposing rollers 14. The rollers 14 are resiliently deformable to enablea secure frictional grip of the instrument or tool shaft 16 of the robotarm 18 between the rollers. The rollers can be made of any suitablematerial. Advantageously, the rollers (or any other engagementmechanism) can comprise a frictional coating, to enhance the frictionalgrip. The rollers (or, again, any other engagement mechanism) canadditionally or alternatively comprise surface undulations, such asprotrusions, recesses and/or ridges, for increasing the ability of therollers 14 to grip the shaft 16. This can prove useful in maintaining agood frictional grip throughout a surgical procedure, when the shaft 16can become covered in fluids common at surgical sites, such as blood.

The rollers 14 are arranged for rotation about an axis extending out ofthe plane of FIG. 2, as indicated by the arrows 20. The engagingmechanism could comprise more than two rollers 14. For example, threerollers could be arranged in a triangular configuration, or four rollerscould be arranged in a square configuration. Other numbers and/orconfigurations of rollers 14 are also possible.

In another example (not shown), the tool shaft comprises exterior ridges(with corresponding recesses between the ridges) or indentations, whichare provided around at least a portion of the circumference of the shaftand extend along at least a portion of the length of the shaft. In someexamples the rollers comprise protrusions spaced about the circumferenceof the rollers to engage with the recesses or the indentations on theshaft. This arrangement can form a rack and pinion type engagingmechanism. This arrangement can provide increased resistance to slippingand can provide increased control over the relative position of thelocator and the shaft.

A distance sensor 26 is provided on a distal end of the robot arm 18. Inthe example illustrated in FIG. 2, the sensor 26 is a laser sensor, andis arranged to determine the distance between the distal end of therobot arm 18 and the locator (as indicated by arrow 28). A communicationmodule remote from the locator (not shown) can transmit the detecteddistance or a movement command to the wireless communications module 22of the locator (this can alternatively, or additionally for example forredundancy, be transmitted by a wired connection (not shown)). Therollers 14 are arranged to be driven by the motor 24 in response to thetransmitted signal.

In another example the sensor 26 is provided on the locator (shownschematically in dashed lines at 30). Providing the sensor 26 on thelocator can enable the locator to be autonomous. In other words thelocator can control itself A power source such as a battery 32 can alsobe provided on the locator. Alternatively or additionally a wiredconnection can provide power to the locator, for example to the motor24.

FIGS. 3(a) and (b) show an alternative configuration of a port carrieror locator 200. The locator 200 shown in FIG. 3 is attached to thedistal end of a robot arm 18. The locator 200 comprises an extensiblemember 34 which carries an interface 36 at its end remote from the robotarm 18. The extensible member can vary in length from the retracted orcontracted configuration shown in FIG. 3(a) to the extendedconfiguration shown in FIG. 3(b).

The port carrier has a motor 38 which can drive the extensible member toextend or contract so as to adopt a desired length. In other words, thedriving of the extensible member 34 by the motor 38 can control thedistance between the locator (and hence the port 40) and the distal endof the robot arm 18. In one example the motor 38 is operatively coupledto a spool 42 about which the extensible member is coiled and to whichit is attached. Driving the spool allows the extensible member to beextended and retracted.

In another example, the spool 42 could be mounted to the port 40 insteadof to the distal end of the robot arm 18. In one example, the motor 38could also be provided on (or attached to) the port 40. Theconfiguration shown in FIG. 3 (where the spool 42 and motor 38 areprovided on the distal end of the robot arm 18) advantageously enablesthe port 40 to remain relatively light in weight. This can make iteasier to control the movement of the port.

In one example, the extensible member 34 is a coiled metal tape. Inother examples, other suitable materials can be used. The tape isconfigured with a cross-sectional shape that resists bowing of the tapeaway from the shaft 16. This enables positional accuracy to bemaintained. For example, the tape may have a generally U-shapedcross-section. Rigidity of motion can be provided by the instrument. Inat least some examples this enables the use of a flexible extensiblemember 34 yet provides rigidity of motion of the interface (and hencethe surgical port). This can mean that the interface is controllablesuch that its position relative to the seat is always determinable.

In one example the spool is resiliently biased towards one of extensionor retraction to assist with extending or contracting the extensiblemember. In some examples, the motor 38 is engagable to assist or counterthe biasing force (in other words the motor can for example generateforce that balances or exceeds the biasing force). In one example thespool is biased by a resilient member such as a spring. In one example,the spool is resiliently biased towards a contracted state to assist indrawing the port 40 towards the distal end of the robot arm 18. In thisexample, the motor 38 can be engaged to balance the biasing force whenthe location of the interface and hence the port 40 is desired to remainconstant with respect to the distal end of the robot arm 18.

The single member is arranged to permit motion over the full extent ofthe linear relative motion of the seat and the interface.

Referring now to FIGS. 4(a) and (b), in another example the extensiblemember is an inflatable bag 44 that carries the interface 36 at its endremote from the robot arm 18. The extensible member can vary in lengthfrom the retracted or contracted configuration shown in FIG. 4(a) to theextended configuration shown in FIG. 4(b).

The port carrier or locator 200 in this example also has a driver 38which can drive the extensible member to extend or contract so as toadopt a desired length. In other words, the driving of the extensiblemember 44 by the motor 38 can control the distance between the interface(and hence the port 40) and the distal end of the robot arm 18. In thisexample the driver 38 may be a pump for controlling fluid pressurewithin the extensible member 44. The pump 38 can control fluid pressurein the inflatable bag 44 by controlling fluid flow through at least onevalve into and/or out of the inflatable bag 44.

For example, to inflate the bag (and move the port 40 further away fromthe distal end of the robot arm 18), the pump 38 can be controlled topump fluid such as gas into the inflatable bag 44. The increase inpressure within the bag 44 can cause it to expand along a portion of thelength of the shaft 16 away from the robot arm 18. To deflate the bag(and move the port 40 towards the distal end of the robot arm 18), thepump 38 can be controlled to pump fluid such as gas out from theinflatable bag 44. The fluid could be pumped back into a fluid store(not shown) or let out into the atmosphere adjacent the locator. Thismay be suitable where the fluid is a gas. Alternatively or additionallyto pumping the fluid out of the bag 44, a valve (which in some examplesis an outlet valve) can be operated to open a fluid communicationchannel to a volume with a lower pressure than that inside the bag 44.For instance, the bag 44 might inflate at an internal pressure aboveatmospheric pressure, and the valve might open to the atmosphere to ventthe fluid so as to allow the bag to deflate. The pump 38 can be used toassist this, which might make it quicker, and to enable the bag 44 toadopt a more contracted configuration than might be possible withventing to atmosphere alone. For example the pump can reduce thepressure in the bag to below ambient or atmospheric pressure.

Conveniently, the instrument shaft 16 passes through the interior of theinflatable bag 44. In this example, the bag 44 is coupled to theinterface 36 in a sealed manner to enclose a sealed volume within thebag 44. Rigidity of the extensible member 44 both in contracted andextended configurations can be provided by the instrument shaft 16.

The inflatable bag 44 (which in some examples could be an inflatablesheath) is in some examples at least part of a sterile drape that isused to at least partially cover at least a portion of a roboticsurgical system. For example, the sterile drape might cover the robotarm 18, and the instrument or tool might extend through the drape.Providing the extensible member 44 as part of the drape can provide amore uniform and/or consistent sterile barrier.

The gas might be carbon dioxide, a source of which may be provided inthe robot arm 18 for insufflation. Using this gas for inflating theinflatable bag 44 as well can reduce the complexity of fluid conduitsneeded within the robot arm 18. Any other suitable fluid could be usedinstead. In another example, air can be pumped into the inflatable bag44 for example from the atmosphere adjacent a portion of the robot arm18, or adjacent the bag 44.

Where a gas suitable for insufflation such as carbon dioxide is used toinflate the inflatable bag 44, the inflatable bag 44 can form a portionof a fluid flow path for insufflating a surgical site. Valves (notshown) can be provided to outlet the gas from the inside of the bag 44through the port 40 and towards the surgical site. In such examples, itis convenient for the inflatable bag 44 to be arranged to inflate atpressures above those used for insufflation. In this way, insufflationof a surgical site can be achieved independently of the state of theextensible member 44.

Where the bag 44 is not inflated, the insufflation gas can simply beallowed to pass through the bag 44. The pressure of the gas will not besufficient to cause the bag 44 to inflate. Where the bag 44 is inflated,a valve such as a bleed valve or regulator valve (not shown) can be usedto restrict gas flow to both ensure a sufficient pressure inside the bag44 for inflation of the bag 44 and to allow gas at an appropriatepressure to be used for insufflation.

In these examples it is convenient if at least one one-way valve isprovided along the fluid flow path between the interior of theinflatable bag 44 and the outlet of the port 40 into the surgical siteto make sure that no contaminants from the surgical site can travelupstream into the bag 44. Alternatively or additionally one or moreone-way valve can be provided in a fluid flow path between the robot arm18 and an inlet into the inflatable bag 44. The inflatable bag 44 may bedisposable, for example along with or as part of the surgical drape.

Referring to the various arrangements described, the driver (such as themotor or pump)is controlled by a motor controller 50 (see FIG. 8). Asthe robot arm moves, the motor controller computes the position and/orlength required of the mechanism 14, 34, 44 in order to keep the port10, 40 in place in an incision in the patient. In this way, the port canbe kept in place without relying on it being attached to the incisionand without it transmitting any significant force to the mc1s10n.

The port carrier 200 shown in FIGS. 3 and 4 has a seat 64 by means ofwhich it is attached to the distal end of the robot arm 18. The seat 64could comprise a clamp which is tightened in position on the arm. Theseat could mate to the robot arm by means of a snap fitting. The seat 64could be screwed on to the arm or attached to it by adhesive. Othermethods of attachment are possible.

The seat is fixed to a part of the robot arm 18 that remains coaxialwith a surgical instrument 16 during surgery. Thus it could be attachedto the robot arm distally of the terminal joint of the robot arm, ordistally of the most terminal joint of the robot arm whose axis is notcoaxial with the instrument. In one example (not shown) there is a jointlocated distally of the attachment. The rotation axis of this joint iscoaxial with the instrument 16.

The extensible member 34, 44 is attached rigidly to the seat 64. In theexamples shown in the figures the extensible member has a linearlyextending configuration which is convenient because it avoids theextensible member taking up excessive space.

The motor 38 can drive the motion of the extensible member in anysuitable way. For example, a rotary motor may drive the spool 42 of theexample shown in FIG. 3 directly, or via a belt. The motor may producelinear drive which can be transformed into rotary drive, for example bya rack and pinion type arrangement amongst others. There could be apneumatic or hydraulic piston which acts analogously to the motor. Therecould be a single motor, piston or other device that provides the entirerange of motion of the mechanism (e.g. the extensible mechanism).Alternatively the mechanism (e.g. the extensible mechanism) could havemultiple drivers such as motors and/or pistons operating in series toprovide the full range of motion.

Referring now to FIG. 5, in one example the locator 200 comprises anarticulated mechanism in the form of an articulated robot arm 60. Aninterface 62 couples one end of the articulated arm 60 to the port 40,and a seat 64 couples the other end of the articulated arm 60 to therobot arm (i.e. the main robot arm 70). The articulated arm 60 isarticulated so as to enable linear relative motion between the interface62 of the articulated arm and the distal end of the robot arm 18. Thearticulated arm comprises at least one articulated joint 66.

In the example shown in FIG. 5 the seat 64 of the articulated arm 60 iscoupled to the main robot arm 70 proximally of the most distal joint 72,but distally of the next most distal joint 72. The articulated arm 60 inthis example comprises one articulated joint 66. In general the numberof articulations or articulated joints 66 needed in the articulated arm60 depends on where the seat 64 is mounted to the main robot arm 70.

The articulated arm 60 has fewer articulations than the main robot arm70. The articulated arm 60 can include one or more types of roboticjoint such as revolute and prismatic joints. The configuration of jointscan be chosen in dependence on the available volume that can be occupiedby the articulated arm 60 and the volume it can sweep out duringmovement, and/or amongst other factors.

A driver (not shown) such as a motor, for example an electric motor, isoperatively coupled to at least one of the at least one articulatedjoint 66 of the articulated arm 60. The motor is configured to apply aforce between the seat 64 and the interface 62 to alter theconfiguration of the articulated arm 60. The at least one articulatedjoint 66 is in one example driven by the motor.

A piston such as a hydraulic or pneumatic piston or other device couldbe used to drive the articulated arm 60. There could be a single motor,piston or other device that provides the entire range of motion of thearticulated arm 60. Alternatively the articulated arm 60 could havemultiple devices operating in series to provide the full range ofmotion.

Further examples of locators will now be described with reference toFIGS. 6 and 7. FIG. 6 shows an articulated support mechanism 80 with abase 84 coupled to a patient support 76 such as a table and an interface82 coupled to a gimbal system 74. In this example the articulatedsupport 80 comprises one joint 86, but in other examples the supportmechanism 80 can comprise a plurality of joints, at least one of whichmay be an articulated joint. The articulated support 80 can include oneor more types of robotic joint such as revolute and prismatic joints.The port 40 is rotatably coupled to the gimbal system 74.

The support mechanism or support arm 80 comprises, in one example, alock or locking mechanism (not shown) which enables at least one jointof the arm to be locked to restrict its movement. In this way thesupport arm 80 can be held firm when locked, then unlocked to enablemanual or motorised movement of the arm, and then locked again when thearm is in the desired position. The locking of the arm enables it toremain firmly located during a surgical procedure, and can preventaccidental or inadvertent motion of the support arm 80.

The articulations of the support arm 80 can be driven in a manneranalogous to the driving of the articulations of the articulated arm 60as described above, but may be separately driven. The driving of thesupport arm 80 may enable the position of the port 40 to be changedbetween surgical procedures, and/or it may enable the position of theport 40 to be changed during a surgical procedure to match at least oneof motion of the robot arm 18 and motion of a patient (such as motioncaused by breathing). This control of the motion of the port 40 canreduce forces acting on the port 40 and hence forces transmitted to theincision in the patient.

In the example shown in FIG. 7 the port 40 is held in place by a belt90. In this example the belt is a solid belt. The solid belt can providestructural rigidity to the system. In other examples the belt may bemore flexible. In such examples, structural rigidity can be provided atleast partially by the tension in the belt holding the belt against anobject such as a patient lying on the patient support 76. Referringagain to FIG. 7, the belt 90 is provided in two portions, each of whichare coupled to the patient support 76 at one end and to the gimbalsystem 74 at the other end.

The gimbal system 74 is driven to keep it (and hence the port 40)pointed in the desired direction. The gimbal system is in one exampledriven by a motor provided on the gimbal system itself The gimbal system74 can be in communication with a remote device such as a portion of therobotic surgical system through a wired connection or through a wirelessconnection or both. The gimbal system may therefore comprise a wiredconnection and/or a wireless communication module (not shown). The wiredconnection may alternatively or additionally be used to provide power tothe gimbal system 74. A local power source such as a battery may beprovided on the gimbal system 74.

The control of the gimbal system 74 and hence of the port 40 is in someexamples independent of any instrument or the robot arm. Thisarrangement can be used to enable fully automatic instrument change: therobot arm can be employed in another action without worrying about theport location or orientation.

When moving an instrument shaft into and/or out of a surgical site, thedistal portion of the robot arm (i.e. that portion of the robot arm towhich the surgical instrument is attached) is typically constrained tomove along one axis (an insertion/removal axis) to avoid exerting forcessuch as lateral forces on the surgical port. Suitably the supportmechanism is arranged to permit motion of the interface in a directionperpendicular to the insertion/removal axis. In other words, the supportmechanism can allow movement of the interface away from the axis alongwhich the surgical instrument is constrained to move during insertionand removal.

Referring again to FIG. 2, in some examples the port for use with any ofthe locators described above comprises an inlet port 100. The inlet port100 is in fluid communication with a chamber 102, which is in fluidcommunication with an outlet port 104. Gas such as carbon dioxide forinsufflation can be provided to a surgical site via the inlet port 100,the chamber 102 and the outlet port 104.

In some examples the chamber 102 comprises another outlet, towards thedistal end of the robot arm. A valve 106 is provided to restrict orprevent the flow of the fluid through this outlet. The valve can be aone-way valve. This can prevent any undesirable build-up of pressurebehind the valve 106. In some examples a one-way valve can be providedalong the flow path from the chamber 102 to the outlet 104. This canrestrict or prevent fluid flow from a surgical cavity into the port.

The ports illustrated in FIGS. 3 to 5 are attached rigidly to the distalend of the extensible member 34, 44 or articulated arm 60. The port canbe a conventional surgical port, or it could be simplified due to thereduced need for the port to hold itself in place in the incision. FIG.9 shows two examples of how the port can be configured. FIG. 9 showscross-sections through the areas around incisions 124 in the skin 123 ofa patient. In the left-hand part of FIG. 6 the port 112 a has an annualinner wall 125 which sits on the inside of the patient's skin radiallyoutward of the incision 124 and an annual outer wall 127 which sits onthe outside of the patient's skin radially outward of the incision 124.The inner wall could be expanded into position once the port has beenlocated in the incision. A central tube 126 runs through the patient'sskin at the incision site and connects the inner and outer walls 125,127. In the right-hand part of FIG. 9 the port 112 b consists simply ofa central tube 126 running through the patient's skin at the incisionsite. It does not extend radially outwards of the incision inside oroutside the skin. In another design the port could be as shown at theleft-hand side of FIG. 9 but without the inner wall 125. This latterdesign is advantageous in that it can easily be inserted into thepatient without the need to stretch the incision to accommodate theinner flange 125 or to have a complex port design in which the innerflange is expandable, but the outer flange 127 can still assist inresisting motion of the port. In each of these examples the port has apart that passes through the patient's skin at the incision site and canthereby maintain separation between the skin and the instrument 16. Theinstrument 16 is inserted through that part of the port.

The surgical instrument 16 extends from the distal end of the arm 18.The instrument could, for example, be a cutting, gripping or sensinginstrument. The instrument extends linearly away from the arm 18. Theinstrument passes through the port 112. In this example the instrument16 is not connected to the port 112 other than via its attachment to thearm 18. Since the instrument is free from the port in this way, lateralmovement of the instrument, for example if its tip deflects when pressedon a hard object, will not be transmitted to the port unless the armitself moves. This reduces the chance of the incision being damagedduring an operation.

In some examples the port carrier does not provide linear travel to theinstrument. It is not linked to the instrument distally of the distalend of the robot arm. It responds to movement of the arm and of theextensible member 34, 44 or articulated arm 60 but not to separatemovement of the instrument.

The main robot arm 70 has a plurality of joints 72 along its length,which allow the position of the distal end of the arm to be movedrelative to the base 78 of the arm. Each joint is equipped with aposition encoder (not shown) which detects the configuration of thejoint. The outputs of the position encoders are passed to the controlunit 50 as indicated at 51 in FIG. 8. The motor may incorporate or beequipped with a position encoder that provides the control unit 50 withinformation indicating the current length of the extensible member 34,44 and/or the current position of the articulated arm 60 or the currentposition of the locator on the shaft 16 (as appropriate). Alternatively,there may be one or more separate position encoders for the extensiblemember 34, 44, the articulated arm 60 and/or the locator mounted on theshaft 16.

The control unit 50 comprises a processor 52 and a memory 53. The memory53 stores in a non-transitory form a program comprising a series ofinstructions for execution by the processor to perform in the mannerdescribed below. The program models the operation of the robot arm sothat based on the outputs from the position encoders the control unitcan estimate the spatial position of the distal end of the arm 18. Whenan operation is to be carried out, an operator puts the robot arm in aninitial configuration and attaches the port to an incision in thepatient with the locator in a suitable configuration to hold the port inthe desired location, for example with the extensible member 34, 44 of asuitable length to run from the robot arm to the port. At this point thecontroller is receiving position information from the position encoders,so it can calculate the position of the distal end of the arm and knowsthe length of the extensible member 34, 44 (in other examples it willknow the position of the distal end of the articulated arm 60, supportarm 80 and/or the locator on the shaft 16).

The operator then operates a user interface control 54 to signal to theprocessor that the current configuration is a reference configuration.Subsequently, during the course of an operation the robot arm will bemoved, and the distance between the distal end of the robot arm and theport will vary. That movement can be computed by the processor 52 usingthe program stored in the memory 53. The processor can thereby determinethe configuration required of the locator, such as the length requiredof the extensible member 34, 44, in order for the port 112 to remain inplace in the incision in the patient. As that configuration changes theprocessor 52 commands the motor via a line 55 in order to cause thelocator to adopt a configuration such that the port remains in place inthe incision.

As the robot arm 18 inserts the instrument into the patient the locatormoves the port towards the robot arm 18 (by controlling the engagingmechanism 14, by contracting the extensible member 34, 44, and/or bycontrolling the articulated arm 60) under the control of the controller50, keeping the port in the correct place. As the robot arm 18 retractsthe instrument from the patient the locator moves the port away from therobot arm 18 (by controlling the engaging mechanism 14, by extending theextensible member 34, 44, and/or by controlling the articulated arm 60)and provides the reaction force to keep the port in place. The motion ofthe engaging mechanism, the extensible mechanism and/or the articulatedmechanism is synchronised in time and in displacement with motion of thearm.

The processor could use additional information. For example, anoperating theatre in which the robot is located could be equipped with asensor 56 that senses motion of the patient. The sensor could sensemotion of the patient remotely, using for instance ultrasound or opticalsignals. In this way, if the incision moves, for example as the patientbreathes, this motion can be taken into account by the processor tocause the port to remain at the position of the incision for the timebeing.

The logic implemented by the processor may be as illustrated in FIGS. 10and 11.

FIG. 10 illustrates the actions following the resetting of the system inresponse to the control 43 being actuated (step 160). The initialposition of the distal end of the robot arm (“D”) is determined (step161), as are the direction in which the distal end of the arm ispointing (step 162) and the configuration of the locator (step 163).This last step can include determining the length of the extensiblemember, determining the location of the locator on the shaft 16,determining the configuration of the articulated mechanism and/ordetermining the configuration of the support arm 80.

Then the position of the port (“P”) can be computed as being the pointoffset by the determined separation in that direction from point D (step164). For this step the controller can be pre-programmed with therelationship between the distal end of the arm and the direction ofextension of the extensible member. The locations of P and optionally Dare stored, for example as Cartesian coordinates (step 165).

FIG. 11 illustrates a control loop, with reference to FIGS. 3 and 4,when the robot is in operation. The new position (“N”) of the distal endof the arm is determined (step 170). A desired length (“L”) isdetermined as the magnitude of the offset between N and D (step 171).Then the motor is controlled to set the length of the extensible memberto be L. This loop is repeated whilst the robot is in operation. Therate at which the loop is repeated will depend on the speed of motion ofthe robot, but it could, for example be repeated 20 times per second orfaster. If the controller has knowledge of motion of the incision, thiscan be taken into account in step 171.

The port carrier could be equipped with one or more force sensors 57that sense force on the port. There could be a single force sensor thatsenses force in the direction coaxial with the instrument. The outputfrom this sensor could be used as an input to the processor in additionto or instead of the inputs discussed above. However, for this sensor toprovide information on the stress on the port applied from the incisionthere needs to be a degree of adherence between the incision and theport, and in many situations it may be preferable for the port to besubstantially freely floating in the incision in the direction parallelto the instrument axis.

In some examples, a surgical robot comprises a robot arm and a locatoras defined above coupled to the robot arm. In some examples the surgicalrobot comprises a surgical tool or instrument coupled to the robot arm.A portion of the surgical tool is, in some examples, arranged to passthrough the surgical port. In some examples, the surgical tool issubstantially unsupported by the locator.

In some examples the surgical instrument comprises an instrument shaftand the locator is coupled to the robot arm by being coupled to theinstrument shaft.

The motion of the engaging mechanism, the extensible mechanism, thearticulated mechanism and/or the support mechanism under the control ofthe control unit 50 can resist any frictional force between instrumentand port. This can help to avoid the port being dislodged from theincision when the instrument moves relative to the patient.

In some examples, the mechanism described above can be lighter and morecompact than some prior designs of port retention mechanism since itdoes not have to support the instrument. This means it can take up lessspace, allowing ports to be placed closer together. This is especiallysignificant for surgical procedures in confined spaces, for example earnose and throat (ENT) surgery.

Since the port does not support the instrument in some examples, theport and the port carrier can be removed from the robot armindependently of the instrument. This means the system can performsurgical procedures with self-securing ports or that do not requireports without unnecessary encumbrance. Similarly, the instrument can beremoved from the robot arm whilst the port remains in place.

In some examples, the extensible mechanism is driven for both elongationand contraction. The extensible mechanism could be biased to itsextended or contracted configuration, for example by one or more elasticelements such as a spring. Then the extensible mechanism could be drivenfor motion in one direction, and motion in the other direction could beprovided or at least assisted by the biasing means.

In some examples, the port carrier is attached to the robot arm near thedistal end of the arm. Conveniently it can be located distally of theterminal joint of the arm, distally of the second most terminal joint ofthe arm or distally of the third most terminal joint of the arm. In oneembodiment it can be attached to the arm between the most distal(terminal) joint of the arm and the second most distal joint of the arm.Conveniently any joints located distally of the attachment of the portcarrier to the arm are such as to be incapable of varying the directionof the axis of the instrument relative to the port carrier. Such jointscould permit linear motion of the instrument along its axis and/orrotation of the instrument about its axis. The axis of the instrumentmay be defined by the direction of elongation of the instrument. Theaxis of the instrument may be defined between (a) the port and (b) oneof the location of attachment of the instrument to the arm and thelocation of attachment of the port carrier to the arm. The instrument isconveniently attached to the arm distally of the location of attachmentof the port carrier to the arm. The port carrier could be locatedelsewhere on the arm. For example it could be located near the base ofthe arm.

The applicant hereby discloses in isolation each individual featuredescribed herein and any combination of two or more such features, tothe extent that such features or combinations are capable of beingcarried out based on the present specification as a whole in the lightof the common general knowledge of a person skilled in the art,irrespective of whether such features or combinations of features solveany problems disclosed herein, and without limitation to the scope ofthe claims. The applicant indicates that aspects of the presentinvention may consist of any such individual feature or combination offeatures. In view of the foregoing description it will be evident to aperson skilled in the art that various modifications may be made withinthe scope of the invention. in place.

1-20. (canceled)
 21. A port locator for a surgical port, for receiving a surgical instrument attached to an articulated robot arm, the port locator comprising: a base for attachment to a portion of a patient support; an interface for coupling to the surgical port; an articulated support mechanism linking the base and the interface, the articulated support mechanism including fewer articulations than the robot arm and permitting at least one of translational and rotational movement of the interface relative to the base; and a controller for controlling at least one of a position and an orientation of the interface relative to the base in dependence on the position of the robot arm.
 22. The port locator as claimed in claim 21, wherein the support mechanism includes a lock having a locked configuration for at least partially restricting movement of the support mechanism and an unlocked configuration for at least partially permitting movement of the support mechanism.
 23. The port locator as claimed in claim 21, wherein the support mechanism includes at least one of an articulated support arm and a belt.
 24. The port locator as claimed in claim 21, wherein the support mechanism includes a rotational mechanism permitting rotation of the interface relative to the base.
 25. The port locator as claimed in claim 24, wherein the rotational mechanism includes a gimbal system.
 26. The port locator as claimed in claim 21, wherein the support mechanism includes a support mechanism driver for altering the configuration of the support mechanism by altering at least one of the translational configuration of the interface relative to the base and the rotational configuration of the interface relative to the base.
 27. The port locator as claimed in claim 21, wherein the support mechanism is arranged to permit motion of the interface in a direction perpendicular to that of a direction of insertion or removal of an instrument shaft through the surgical port.
 28. The port locator as claimed in claim 21, in which the support mechanism permits solely linear relative motion of the base and the interface.
 29. The port locator as claimed in claim 21 having a surgical port attached to the interface.
 30. The port locator as claimed in claim 21, wherein the controller includes a processor configured to estimate the position of a part of the robot arm and to set the position of the base relative to the interface in dependence on the estimated position.
 31. A surgical port assembly comprising: a port locator for a surgical port, for receiving a surgical instrument attached to an articulated robot arm, the port locator including: a base for attachment to a portion of a patient support; an interface for coupling to the surgical port; an articulated support mechanism linking the base and the interface, the articulated support mechanism comprising fewer articulations than the robot arm and permitting at least one of translational and rotational movement of the interface relative to the base; and a controller for controlling at least one of a position and an orientation of the interface relative to the base in dependence on the position of the robot arm; and a surgical port unitarily formed with the interface of the port locator.
 32. A surgical robot comprising: a robot arm and a port locator for a surgical port, for receiving a surgical instrument attached to an articulated robot arm, the port locator being coupled to the robot arm and comprising: a base for attachment to a portion of a patient support; an interface for coupling to the surgical port; an articulated support mechanism linking the base and the interface, the articulated support mechanism including fewer articulations than the robot arm and permitting at least one of translational and rotational movement of the interface relative to the base; and a controller for controlling at least one of a position and an orientation of the interface relative to the base in dependence on the position of the robot arm.
 33. The surgical robot as claimed in claim 32 including a surgical tool or instrument attached to the robot arm, wherein a portion of the surgical tool is arranged to pass through the surgical port.
 34. The surgical robot as claimed in claim 33, wherein the surgical tool is substantially unsupported by the port locator.
 35. The surgical robot as claimed in claim 32 including a surgical tool or instrument with an instrument shaft, wherein the port locator is coupled to the robot arm by being coupled to the instrument shaft.
 36. The surgical robot as claimed in claim 32, wherein the controller includes a processor configured to estimate the position of a part of the robot arm and to set the position of the base relative to the interface in dependence on the estimated position. 